Living Diatom Microalgae for Desiccation-Resistant Electrodes in Biophotovoltaic Devices.

Strategies of renewable energy production from photosynthetic microorganisms are gaining great scientific interest as ecosustainable alternatives to fossil fuel depletion. Green microalgae have been thoroughly investigated as living components to convert solar energy into photocurrent in biophotovoltaic (BPV) cells. Conversely, the suitability of diatoms in BPV cells has been almost completely unexplored so far, despite being the most abundant class of photosynthetic microorganisms in phytoplankton and of their good adaptability and resistance to harsh environmental conditions, including dehydration, high salinity, nutrient starvation, temperature, or pH changes. Here, we demonstrate the suitability of a series of diatom species (Phaeodactylum tricornutum, Thalassiosira weissflogii, Fistulifera pelliculosa, and Cylindrotheca closterium), to act as biophotoconverters, coating the surface of indium tin oxide photoanodes in a model BPV cell. Effects of light intensity, cell density, total chlorophyll content, and concentration of the electrochemical mediator on photocurrent generation efficiency were investigated. Noteworthily, biophotoanodes coated with T. weissflogii diatoms are still photoactive after 15 days of dehydration and four rewetting cycles, contrary to analogue electrodes coated with the model green microalga Dunaliella tertiolecta. These results provide the first evidence that diatoms are suitable photosynthetic microorganisms for building highly desiccation-resistant biophotoanodes for durable BPV devices.

A melanin-like polymer bearing phenylboronic units as a suitable bioplatform for living cell display technology.

Surface display of functional groups with specific reactivity around living cells is an emerging, low cost and highly eco-compatible technology that serves multiple applications, ranging from basic biochemical studies to biomedicine, therapeutics and environmental sciences. Conversely to classical methods exploiting hazardous organic synthesis of precursors or monovalent functionalization via genetics, here we perform functional decoration of individual living microalgae using suitable biocoatings based on polydopamine, a melanin-like synthetic polymer. Here we demonstrate the one-pot synthesis of a functional polydopamine bearing phenylboronic units which can decorate the living cell surfaces via a direct ester formation between boronic units and surface glycoproteins. Furthermore, biosorption of fluorescent sugars on functionalized cell membranes is triggered, demonstrating that these organic coatings act as biocompatible soft shells, still functional and reactive after cell engineering.

Lipopeptides as tools in catalysis, supramolecular, materials and medicinal chemistry.

Lipopeptides are amphiphilic peptides in which an aliphatic chain is attached to either the C or N terminus of peptides. Their self-assembly - into micelles, vesicles, nanotubes, fibres or nanobelts - leads to applications in nanotechnology, catalysis or medicinal chemistry. Self-organization of lipopeptides is dependent on both the length of the lipid tail and the amino acid sequence, in which the chirality of the peptide sequence can be transmitted into the supramolecular species. This Review describes the use of lipopeptides to design synthetic advanced dynamic supramolecular systems, nanostructured materials or self-responsive delivery systems in the area of medical biotechnology. We examine the influence of external stimuli, the ability of lipopeptide-derived structures to adapt over time and their application as medicinal agents with antibacterial, antifungal, antiviral or anticancer activities. Finally, we discuss the catalytic efficiency of lipopeptides, with the aim of building minimal synthetic enzymes, and recent efforts to incorporate metals into lipopeptide assemblies.

Drug Delivery through Epidermal Tissue Cells by Functionalized Biosilica from Diatom Microalgae.

Diatom microalgae are a natural source of fossil biosilica shells, namely the diatomaceous earth (DE), abundantly available at low cost. High surface area, mesoporosity and biocompatibility, as well as the availability of a variety of approaches for surface chemical modification, make DE highly profitable as a nanostructured material for drug delivery applications. Despite this, the studies reported so far in the literature are generally limited to the development of biohybrid systems for drug delivery by oral or parenteral administration. Here we demonstrate the suitability of diatomaceous earth properly functionalized on the surface with n-octyl chains as an efficient system for local drug delivery to skin tissues. Naproxen was selected as a non-steroidal anti-inflammatory model drug for experiments performed both in vitro by immersion of the drug-loaded DE in an artificial sweat solution and, for the first time, by trans-epidermal drug permeation through a 3D-organotypic tissue that better mimics the in vivo permeation mechanism of drugs in human skin tissues. Octyl chains were demonstrated to both favour the DE adhesion onto porcine skin tissues and to control the gradual release and the trans-epidermal permeation of Naproxen within 24 h of the beginning of experiments. The evidence of the viability of human epithelial cells after permeation of the drug released from diatomaceous earth, also confirmed the biocompatibility with human skin of both Naproxen and mesoporous biosilica from diatom microalgae, disclosing promising applications of these drug-delivery systems for therapies of skin diseases.

Polydopamine coating of living diatom microalgae.

Many microorganisms produce specific structures, known as spores or cysts, to increase their resistance to adverse environmental conditions. Scientists have started to produce biomimetic materials inspired by these natural membranes, especially for industrial and biomedical applications. Here, we present biological data on the biocompatibility of a polydopamine-based artificial coating for diatom cells. In this work, living Thalassiosira weissflogii diatom cells are coated on their surface with a polydopamine layer mimicking mussel adhesive protein. Polydopamine does not affect diatoms growth kinetics, it enhances their resistance to degradation by treatment with detergents and acids, and it decreases the uptake of model staining emitters. These outcomes pave the way for the use of living diatom cells bearing polymer coatings for sensors based on living cells, resistant to artificial microenvironments, or acting as living devices for cells interface study.

New antimicrobial self-assembling short lipopeptides.

Lipopeptides are an exceptional example of amphiphilic molecules that self-assemble into functional structures with applications in the areas of nanotechnology, catalysis or medicinal chemistry. Herein, we report a library of 21 short lipopeptides, together with their supramolecular characterization and antimicrobial activity against both Gram-negative (E. coli) and Gram-positive (S. aureus) strains. This study shows that simple lipoamino acids self-assemble into micellar or vesicular structures, while incorporating dipeptides capable of stablishing hydrogen bonds results in the adoption of advanced fibrilar structures. The self-assembly effect has proven to be key to achieve antimicrobial activity.